Optical devices having improved temperature stability

Abstract

Optical devices using non-centric crystals, such as lithium niobate, and methods for making and using the devices, are provided. The devices provide improved temperature stability as compared to conventional devices using non-centric crystals. The improved temperature stability is provided by etching the surface of a non-centric crystal to a depth of less than about 300 angstroms. The devices and methods of the invention reduce the magnitude of change in bias voltage required to maintain an optical crystal at a pre-selected operating point.

What is claimed is:  
     
       1. A method for reducing the pyroelectricity of a non-centric crystal comprising etching the surface of the crystal to a depth of less than about 300 angstroms. 
     
     
       2. The method of claim  1  wherein said crystal comprises a waveguide. 
     
     
       3. The method of claim  1 , further comprising depositing a dielectric buffer layer onto said surface. 
     
     
       4. The method of claim  1  wherein the depth of said etching is less than about 275 angstroms. 
     
     
       5. The method of claim  1  wherein the depth of said etching is less than about 250 angstroms. 
     
     
       6. The method of claim  1  wherein the surface of said crystal, following said etching step, has a surface defect density of less than about 5×10 6  defects per square centimeter. 
     
     
       7. The method of claim  1  wherein the crystal comprises a material selected from the group consisting of lithium niobate, barium titanate, lead titanate, potassium lithium niobate, and calcium niobate. 
     
     
       8. The method of claim  7  wherein the crystal comprises lithium niobate. 
     
     
       9. The method of claim  3  wherein the buffer layer comprises indium oxide. 
     
     
       10. The method of claim  9  wherein the buffer layer comprises a dopant comprising indium oxide in silicon dioxide. 
     
     
       11. An optical device comprising a pyroelectric non-centric crystal having an etched surface for reducing crystal pyroelectricity and a voltage source for applying a bias voltage to said device, wherein the depth of said etching into said surface is less than about 300 angstroms. 
     
     
       12. The device of claim  11  wherein the depth of said etching is less than about 275 angstroms. 
     
     
       13. The device of claim  11  wherein the depth of said etching is less than about 250 angstroms. 
     
     
       14. The device of claim  11  wherein the surface of said crystal has a surface defect density of less than about 5×10 6  defects per square centimeter. 
     
     
       15. The optical device of claim  11  wherein said bias voltage is variably applied as required to maintain the operation of said optical device. 
     
     
       16. The optical device of claim  11  wherein said bias voltage varies by less than about 1 volt corresponding to a temperature change of about 70° C. 
     
     
       17. The device of claim  11  wherein said bias voltage varies by less than about 0.7 volt. 
     
     
       18. The device of claim  11  wherein said bias voltage varies by less than about 0.5 volt. 
     
     
       19. The optical device of claim  11  further comprising an optical modulator operable to modulate an input light wave according to an input signal at an operating point which is determined by a bias voltage. 
     
     
       20. The optical device of claim  11  further comprising a detector that detects a deviation of said operating point from a selected optimal operating point based on an output of said optical modulator. 
     
     
       21. The device of claim  11  wherein said crystal comprises lithium niobate. 
     
     
       22. The device of claim  11  wherein said crystal further comprises indium oxide. 
     
     
       23. A method of manufacturing an optical device comprising: 
       providing a non-centric electro-optic crystal;  
       forming a waveguide in the non-centric electro-optic crystal;  
       etching the surface of the crystal to a depth of less than about 300 angstroms;  
       depositing a buffer layer onto the etched surface of the crystal;  
       forming a charge dissipation layer on the buffer layer; and  
       attaching one or more electrodes to the crystal.  
     
     
       24. The method of claim  23  wherein the depth of said etching is less than about 275 angstroms. 
     
     
       25. The method of claim  23  wherein the depth of said etching is less than about 250 angstroms. 
     
     
       26. The method of claim  23  wherein said buffer layer comprises indium oxide. 
     
     
       27. The method of claim  23  wherein said buffer layer comprises indium oxide-doped silicon dioxide. 
     
     
       28. The method of claim  23  wherein said etched surface has a surface defect density of less than about 5×10 6  defects per square centimeter. 
     
     
       29. The method of claim  23  wherein said electrodes comprise gold. 
     
     
       30. A method for reducing pyroelectricity of a non-centric crystal comprising the steps of: 
       forming a waveguide on said crystal; and  
       subsequently etching a surface of the crystal to a depth of less than about 300 angstroms.